public class Test {
    public class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode() {}
     TreeNode(int val) { this.val = val; }
      TreeNode(int val, TreeNode left, TreeNode right) {
         this.val = val;
         this.left = left;
          this.right = right;
      }
  }
    public boolean isSymmetric(TreeNode root) {
        if(root == null){
            return true;
        }
        return isSymmetricChild(root.left,root.right);
    }


    public boolean isSymmetricChild(TreeNode p,TreeNode q){
        if(p == null && q != null || q == null && p != null){
            return false;
        }
        if(p == null && q ==null){
            return true;
        }
        if(p.val != q.val){
            return false;
        }

        return isSymmetricChild(p.left,q.right) && isSymmetricChild(p.right,q.left);
    }
}
